A battery pack described in Japanese Laid-open Patent Publication 2014-203704 is shown in FIG. 27, and comprises a box-shaped housing 102 that stores a plurality of battery cells. Left and right sliding rails 103, which are configured such that the pair slidably mates with a battery-mounting part (not shown) of a power tool or a battery-mounting part (not shown) of a charger, are provided on an upper surface of the housing 102. In addition, a positive-terminal slit 105p and a negative-terminal slit 105n are provided on inner sides, in a width direction, of the left and right sliding rails 103. A positive terminal and a negative terminal of battery-side, electric-power terminals are provided on inner sides of the slits 105p, 105n, respectively. In addition, signal connectors (terminals) 107 are provided between the positive-terminal slit 105p and the negative-terminal slit 105n. 
When the battery pack 100 has been slid onto and thereby connected to the battery-mounting part of the power tool, the positive terminal and the negative terminal of the battery pack 100 are electrically connected to the positive terminal and the negative terminal, respectively, of the power tool. In the alternative, when the battery pack 100 has been slid onto and thereby connected to the battery-mounting part of the charger, the positive terminal and the negative terminal of the battery pack 100 are electrically connected to the positive terminal and the negative terminal, respectively, of the charger. In addition, the signal connectors 107 of the battery pack 100 are connected to the signal connectors (not shown) of the charger.